Night Photography Explored – Part 2: The Milky Way Galaxy

For millenia, people have gazed upon the Milky Way Galaxy in awe of its consistent streak through the night sky. It remains the symbol of enigmatic wonderment for both experienced and casual night sky observers. Thus, it is also one of the first night sky objects that people want to photograph, especially if they’ve taken the time to drive out to the middle of nowhere to see it, which leads to the first requirement.

Find a Dark Sky

In order to properly photograph the Milky Way, the first and most important step is to find a dark sky. If you live in a large city, you have some driving to do. In this case, you may want to consider camping, or staying in a nearby smaller town. The general rule of thumb is that you want to be at least 10 miles away from light pollution caused by urban areas. Of course, if that urban area is several million people large, 10 miles is not going to make much of a difference. A good web-based tool to bookmark can be found here:

Overlayed onto a Google Map is a map of light pollution. This allows you see how far you need to go to get to a truly dark site, which is covered in the darkest shade of black. This will give you the most vivid view of the Milky Way you can find. If a completely dark area is not nearby you, you can still accomplish great shots of the Milky Way as long as you’re clear of any blue regions. If blue or green is all you have immediate access to, you’ll still get the Milky Way in your shots, but light pollution will be very evident.

Composition and Camera Settings

As mentioned in Part 1, and especially with photographing the Milky Way Galaxy, all rules of daytime photography are useless. You won’t be using f/16 to capture this landscape and you won’t be following the rule of thirds. If you do, you will often find yourself with a large, black void at the bottom of the photo which leads to unappealing empty space filling your photo. For this reason, it’s good to have something silhouetted at the base of the photo to anchor the starscape, but too much will leave that empty and undesirable void in your photo that could have been used to capture more of the night sky.

For your aperture, this is where you want a lens that can open up very wide: f/2.8 or less, ideally. In some cheaper lenses, opening up the aperture to its widest will produce some harsh distortion around the edges, so some test shots might help to see where the lowest aperture you can get away with is. This is where investing in a good lens becomes very helpful. The lenses mentioned in Part 1 all work very well for this particular branch of night photography.

Once you’ve dialed in the aperture, next comes the ISO. Many newer cameras are allowing unprecedented ISO ranges, which is excellent news for low-light photography. However it’s important to note that you should never turn your ISO up to the highest setting. It doesn’t do any harm to experiment with, but turning it that high will often produce too much noise to effectively use for any real purpose, other than a lo-res JPEG file. For that reason, it’s best to find where it maxes out, and then bring it back a few steps. Depending on your camera model, it might take a bit of experimenting with, but eventually you’ll find how high of an ISO you can get to without producing more noise than you can clean up in post-processing. For example, if your ISO range maxes out at 12,800, a safe ISO to stick with in night photography (depending on nearby sources of light pollution) would be 5,000 or so. If the ISO maxes out at 25,600, pushing 12,800 isn’t too big of a stretch. In this sense, the noise produced is arbitrary depending on the highest setting available.

Your camera’s ISO capabilities and the lens’ aperture that you’re able to get down to will determine what kind of a shutter speed you can get away with. Unlike with daytime photography, there is no sunny f/16 rule. Light varies much more subtly depending on light pollution, moon phase, position of the Milky Way, etc. Therefore, determining the shutter speed can be a bit more of a narrowing down process. It should be as low as possible, but still producing a healthy histogram toward the middle-left or middle of the graph. Again, with daytime shooting, many people would recommend “exposing to the right” of the histogram, but in this case, the bulk of the right side will be stars and the Milky Way, and you want to preserve some contrast between the darkness of the night sky and the bright objects against it. Most of the time, 20 seconds is a good place to start, but if your aperture is very low and you can get away with a relatively higher ISO, you’ll want to bring the shutter speed down to 15, or maybe even 10 seconds. Conversely, if your aperture is too high and you can’t get away with a high ISO, you might have to push it up to 30 seconds. Going beyond that is strongly discouraged not only because you’ll have to switch to the Bulb (B) setting, but also because once you exceed 20 or 30 seconds, you may begin to notice the stars trailing in your shot. This may be the desired effect you’re going for, but leaving the shutter open for too long produces lots of sensor noise that can be very tricky to clean up. Though there are tricks in Photoshop to do just that, the easiest way to make star trails will be discussed in a future section. To ensure the stars do not leave streaks in the sky, divide 600 by your focal length, and you’ll find the maximum shutter speed allowed before the stars start to leave trails. For example, if your focal length is 24mm, then 600 divided by 24 will give you 25, the value for the shutter speed that you should remain below. With a wider lens, such as 14mm, you obviously have much less to worry about: 600/14=42.9, meaning you could do a 40 second exposure before noticing star trails.

In terms of composition, as mentioned, the rule of thirds won’t necessarily apply as much. With many current setups, a dark sky exposure will yield a silhouetted foreground with all the interesting information in the photo occurring just above that silhouette in the stars and Milky Way. If you were to follow the rule of thirds in this case, you’d be left with a large, uninteresting mass of blackness in your photo, detracting from the whole reason you went out in the middle of the night in the first place. For this reason, it’s best to simply have a small sampling of the foreground to anchor the photo to some scene. Without something ground-based in the foreground, you’ll simply have a sky filled with stars, which can be nice in its own way, but without getting deeper objects such as other galaxies or nebulae as the focal point of the shot (which is saved for another section), it won’t have anything relative to create the drama you might be hoping for. It would be the equivalent of just photographing a few clouds in the sky with nothing else around them.

With some newer cameras that can push higher ISOs relatively easily, you’ll begin to notice that your foreground is getting lit up from nothing more than the light from the Milky Way and the stars themselves. In this case, you’ll have a little bit of extra flexibility in your composition. This will allow you to include a little more of the mountain peak that might be in your foreground, for example, or more of the open prairie, or wherever you find yourself for night photography.

Airglow

From time to time, in a completely dark sky, you’ll notice a green glow in your photos, such as the larger image at the top of this post and just above. For most, it’s disappointing to learn that this is in fact not the northern (or southern) lights, but in fact, a similar phenomenon called airglow. Put simply, it’s remnants of chemical reactions from molecules in the atmosphere colliding with ultraviolet radiation from sunlight. The more sensitive your equipment, the easier you’ll pick it up. Likewise, the higher you are above the ground (such as up in the mountains looking over a large valley), the more interesting patterns you’ll see in the airglow. It may not be the northern lights, but it’s the next best thing, and if you pick it up, it’s definitely worth working into your shot!

This should give you all the information you need to capture a glowing Milky Way Galaxy in the sky! Head out and see what you can capture and most importantly, experiment around with some new ideas that come to your head. The great thing about digital is that it costs nothing to try something new and different.